1. Field of the Invention
The invention relates to a method of fuel injection in multicylinder engines. A fuel pre-pressure is generated in order to convey the fuel inside an inertia pipe via electromagnetically or mechanically controlled valves in the acceleration pipes. This occurs by recirculating the fuel to the reservoir via a return line, and subsequently shutting off the valve, in order to provoke a steep pressure rise by water hammer effect. Each injection nozzle associated with a shutoff valve is supplied with a high-pressure wave. The invention also pertains to a device for carrying out the method. Such technical solutions are required mainly for injecting fuel in internal combustion engines. Preferred fields of application are multicylinder gas engines with Diesel pilot injection, multicylinder compression ignition engines, multicylinder spark ignition engines, and multicylinder engines for the use of alternative fuels.
2. The Prior Art
Multicylinder engines are predominantly equipped with fuel pumps, which are driven by camshafts. The injection rate supplied to the operating cylinders has, in this connection, a marked dependence upon the engine speed with respect to droplet size and spray penetration length. On the other hand, in common rail systems, a constant fuel pressure at maximum value is always prevailing in the rail or overall system up to the injection nozzles. The maximum pressure, however, is only required temporarily during injection of the fuel due to the opening of one or a plurality of electromagnetically controlled injection nozzles.
In this case, the droplet size as well as the properties of the fuel jet remain the same irrespective of the engine speed. However, the fuel high-pressure realized by the pump or pumps is exploited only to a minor extent, leading to a disadvantageous energy balance. For example, in a four-cylinder four-stroke engine with a speed of 3000 revolutions per minute, the cycle period for consecutive injections is 40 ms. The duration of injection per injection period, however, maximally comes to only 2 ms, which corresponds with an energetic utilization of 5% at the most.
Proposals for technical solutions are known according to which provision is made for utilizing the water hammer principle for supplying the high-pressure wave required in one-cylinder engines for injecting the fuel into the operating cylinder. In this context, the pre-pressure required from the fuel pump is limited to a fraction of the fuel pressure needed on the respective injection nozzle. For exploiting this principle in multicylinder engines, the number of fuel pump drives, fuel pumps, as well as fuel pre-pressure lines and fuel return lines correspond to the number of engine cylinders.
In the case of cam- or camshaft-operated fuel pumps of the customary type, the drawbacks of the known solution for fuel injection substantially consist of the dependence of droplet size and spray characteristics on the engine speed. On the other hand, in the case of common rail systems, the dependence of the spray characteristics on the engine speed is avoided, but at the expense of unacceptable energetic efficiency because the high-pressure made available over the entire cycle period instead of the only-injection-duration.
If the water hammer principle, which is known for one-cylinder engines, is applied for multicylinder engines, the requirements with respect to machine and control engineering would multiply because of the required multitude of fuel pumps to be used, implicating as well the same number of fuel feed and fuel return lines to the high-pressure units. This leads to increased cost as well as to impairment of the size/performance ratio.
Therefore, it is an object of the invention to overcome the drawbacks of the known state of art. The goal is a technical solution which, with high energetic efficiency and low machine engineering expenditure, offers the possibilities for improving the size/performance ratio and the price/performance ratio in the manufacture of multicylinder engines.